1. Field of the Invention
The invention relates generally to hazardous waste disposal employing known solidification processes and particularly relates to methods for controlling the release of ammonia from waste containing ammonia nitrogen during solidification processing and also from solid waste so processed.
2. Description of the Prior Art
Storage of certain chemical wastes resulting from the manufacture of industrial and agricultural chemicals as well as the destruction of materials such as obsolete chemical munitions has long presented a serious waste management problem. Chemical wastes of this nature including pesticide residues have long been simply held in evaporation basins which now contain a complex mixture of materials having significant concentrations of chloride, organic carbon, ammonia-nitrogen, and various toxic substances such as aldrin, arsenic and cyanide with the principal dissolved salts being ammonium and sodium sulfates and chlorides. Significant quantities of copper are also present in these existing waste-containing basins. Liquid in such basins contacts precipitated solids in the basins and, as evaporation continues, approaches an equilibrium condition beyond which continued volume reduction by evaporation becomes negligible. Due to the complexity of the chemical mixtures found in these evaporation basins, detoxification treatments are largely ineffective and/or uneconomical. Accordingly, solidification processing for landfill storage is the method of choice for eliminating the undesirable storage of these toxic wastes in open basins. While a number of solidification technologies exist, the typical solidification process involves mixing of a setting agent or agents with the waste to form a hard, durable product which is substantially insoluble in water and in which the waste contaminants are entrapped in a solidified mass. A number of commercially available solidification processing techniques are in use at the present time with the most common setting agents being Portland cement, flyash, kiln dust, lime, soluble silicates, gypsum and various combinations of these materials.
Patented examples of solidification processes include U.S. Pat, No. Re. 29,783 to Smith et al. which teaches the addition of lime, sulfate ions and flyash as a source of aluminum ions to waste to form a solid product intended for landfill storage. Kupiec et al., in U.S. Pat. No. 4,149,968, mixes bentonite clays and Portland cements with aqueous waste in order to form an insoluble, solidified waste material. In U.S. Pat. No. 3,837,872, Connor proposes the solidification of aqueous waste with alkali metal silicates. Manchak, Jr. in U.S. Pat. Nos. 4,028,240 and 4,079,003 proposes the mixing of lime with oil sump waste and the like for solidification and ultimate storage in landfill sites. A number of additional techniques exist including techniques described in the foreign patent literature, such as United Kingdom 1,485,625 and examples also exist in the non-patent literature itself. Solidification technologies are generally classified by the United States Patent Office in Class 210, subclass 751, as well as other classifications within the patent classification system.
Solidification processing of the toxic waste referred to above usually results in the undesirable evolution of ammonia vapors due to the fact that the usual setting agents involved in solidification processing are alkaline materials. As a result, the products of solidification processing are basic on the pH scale with the final pH of the solidified product depending on the type and amount of setting agent used. This evolution of ammonia gas during solidification processing represents a substantial air quality problem as well as a health safety hazard for workers involved in processing of the toxic wastes. While ammonia evolution during processing is in and of itself a substantial problem, it is also the case that a continued release of ammonia gas in the solidified waste itself also presents problems once the solidified waste is relocated to a landfill site. The evolution of ammonia gas from a landfill site presents an unacceptable air quality hazard and cannot be tolerated.
The present invention provides a method for pretreatment of toxic waste of the nature described above prior to solidification processing such as by means of the technology referred to hereinabove. In particular, the present method intends the sequestering of ammonia off-gassing by chemical conversion of the ammonia into a solid precipitant which is essentially insoluble in water. The prior art does not describe such a teaching. As an example of prior art teachings, Thompson, in U.S. Pat. No. 4,460,555 describes a water-insoluble magnesium phosphate product which can be used to treat sewage waste water to form MgNH.sub.4 P0.sub.4. The magnesium phosphate product described by Thompson is formed from a buffered magnesium hydroxide solution in phosphoric acid. However, Thompson does not describe a process capable of sequestering ammonia off-gassing from toxic waste materials, during solidification processing nor does Thompson describe the particular process taught herein. Noshimura et al., in U.S. Pat. No. 4,219,441, and Dobbs, in U.S. Pat. No. 3,948,769, describe methodology for removal of ammonium nitrogen from waste water. Nashimura et al. utilize a zeolite and are primarily concerned with regeneration of the zeolite. Dobbs describes the use of a hydrous zirconium oxide ligand exchanger which has been conditioned with a salt of a metal such as CuS0.sub.4 capable of forming a complex with ammonia.
The prior art does not provide a solution to the problem of ammonia off-gassing occurring during solidification processing of hazardous waste as well as during the storage of solidified products so produced which contain ammonia.